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One irritating little amp - VM 557
#8

Interesting amp, TV Man.  V-M was no Fisher, but it looks that this was a serious attempt at HiFi. I take that the output tubes are EL84 / 6BQ5s.  These things can outdo 6V6s.  These were likely in the Vox amps used by the Beatles, Kinks, rolling Stones, etc.  These can develop as much as 17W at 300V in Push Pull.  So this is why the amp rocks.

Seems that there are many places for bad things to happen.  What is S7 labeled as?  Seems to be part of the feedback circuit.  (many inexpensive amps did not use feedback.  Wonder that if this switch opens, negative feedback is affected.  Wonder if the thing breaks into oscillation.  New sockets and plenty of Glyptol on the output tube plate and screen connections?  Use ceramic sockets?  Seems that C11 can do funky things if it leaks.  I totally do not understand the phase inverter circuit.  Maybe change it to a cathodyne phase invertor (See your "Classic Dynaco" circuit).

VM did do some strange things, but they DID sound good.  We had V-M 316 that Dad bought for Mom for Christmas 1963.  Mom loved the thing for many years until I came up with better stuff and she lost interest in records.  It deteriorated, the speakers were glombed for the garage, ersatz guitar amps, etc., and of course, the cartridge and capstan went sour.  I should have grabbed the amp before we threw the case out after Dad sold the house (Mom passed away several years before at the young age of 54).  This Phono did a lot with a little.  Stereo phone with volume, balance, bass, treble controls.  No power transformer.  Amp was 2 Single end 50L6s and a 12AX7.  Solid State voltage doubler circuit.  Each speaker cabinet had 2 different 6" speakers.  No tuned port or anything like that.  I suppose that with 180V on the 50L6 plates, the thing developed 5W per channel. 

Had friends who had a Maggot Box OOPS, Magnavox suitcase.  Mono, 8" speaker (can't remember if there was a tweeter or just the "whizzer" cone on a single 8" speaker.  Amp was 12AX7, 2 50C5s and solid state voltage doubler.  The thing did put out. 

Had a Magnavox console with a 24" B/W TV, Collaro changer (I substituted a Garrard with a magnetic cartridge and a radio shack box preamp)  AM FM radio (not MPX Stereo or even AM A FM B).  The power amp was 2 SE 6BQ5s and a 12AX7 with 5Y3 rectifier.  2 old school 12" full range speakers (similar to the ones in early post war console radios) with 3" tweeters.  Sounded pretty nice but boomy.  parted out when the CRT died, was an oddball 24" that I could not sub with the 23" tubes that were in sets that found their way to the street.  Still have the power amp chassis.

Had the power amp from a Magnavox AM FM Phono mono console.  1 12AX7 driving 4 6V6s.  Brother in Law had a similar set but he trashed it before I could get the amp chassis from it.  My amp chassis was long gone but I saved the output transformer from it.  Shame, that could have made an impressive amp.  But I DO have 2 Bogen Challengers.  One has 4 7868s, the other has 4 7591s.  If the output transformers are the same, this would make a great Stereo Amp or 2 "MonoBlocks".

And all the others that got away, especially when Dad ordered a "purging".

"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis

Best Regards, 

MrFixr55


Messages In This Thread
One irritating little amp - VM 557 - by TV MAN - 03-05-2025, 08:57 PM
RE: One irritating little amp - VM 557 - by David - 03-05-2025, 09:39 PM
RE: One irritating little amp - VM 557 - by morzh - 03-05-2025, 09:51 PM
RE: One irritating little amp - VM 557 - by Arran - 03-06-2025, 03:45 AM
RE: One irritating little amp - VM 557 - by MrFixr55 - 05-07-2025, 07:31 AM



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